EASY

Earn 100

List the applications of photoelectric effect.

Important Questions on Dual Nature of Radiation and Atomic Physics

HARD

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

The magnetic field associated with a light wave is given, at the origin, by

B = B_{0} [\sin (3.14 \times 10^{7}) c t + \sin (6.28 \times 10^{7}) c t] .

If this light falls on a silver plate having a work function of

4 .7 eV,

what will be the maximum kinetic energy of the photoelectrons?

(c = 3 \times 10^{8} m s^{- 1}, h = 6 .6 \times 10^{- 34} J s)

HARD

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

In a historical experiment to determine Planck's constant, a metal surface was irradiated with light of different wavelengths. The emitted photoelectron energies were measured by applying a stopping potential. The relevant data for the wavelength

(λ)

of incident light and the corresponding stopping potential

(V_{0})

are given below:

$λ (μ m)$	$V_{0} (v o l t)$
0.3	2.0
0.4	1.0
0.5	0.4

Given that

c = 3 \times 10^{8} m s^{- 1} and e = 1.6 \times 10^{- 19} C,

Planck's constant (in units of

J s

) found from such an experiment is :

HARD

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

A metal plate of area

1 \times 10^{- 4} m^{2}

is illuminated by a radiation of intensity

16 mW m^{- 2}

. The work function of the metal is

5 eV .

The energy of the incident photons is

10 eV

and only

10 %

of it produces photo electrons. The number of emitted photo electron per second and their maximum energy, respectively, will be:

[1 eV = 1.6 \times 10^{- 19} J]

EASY

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

Consider the following statements regarding the photoelectric effect experiment:

(I) Photoelectrons are emitted as soon as the metal is exposed to light.

(II) There is a minimum frequency below which no photo-current is observed.

(III) The stopping potential is proportional to the frequency of light.

(IV) The photo-current varies linearly with the intensity of the light.

Which of the above statements indicate that light consists of quanta (photons) with energy proportional to frequency?

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

Light of wavelength

500 nm

is incident on a metal with work function

2.28 eV.

The de Broglie wavelength of the emitted electron is:

EASY

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

When a certain photosensitive surface is illuminated with a monochromatic light of frequency

ν,

the stopping potential of the photo current is

- \frac{V_{0}}{2} .

When the surface is illuminated by monochromatic light of frequency

\frac{ν}{2},

the stopping potential is

- V_{0} .

The threshold frequency for photoelectric emission is

HARD

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

Light of wavelength $λ_{p h}$ falls on a cathode plate inside a vacuum tube as shown in the figure. The work function of the cathode surface is $ϕ$ and the anode is a wire mesh of conducting material kept at a distance $d$ from the cathode. A potential difference $V$ is maintained between the electrodes. If the minimum de Broglie wavelength of the electrons passing through the anode is $λ_{e},$ which of the following statement(s) is(are) true ?
Question Image

HARD

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

The radiation corresponding to

3 \to 2

transition of hydrogen atom falls on a metal surface to produce photoelectrons. These electrons are made to enter a magnetic field of

3 \times 1 0^{- 4} T

. If the radius of the largest circular path followed by these electrons is 10.0 mm, the work function of the metal is close to :

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

Following graphs show the variation of stopping potential corresponding to the frequency of incident radiation

(f)

for a given metal. The correct variation is shown in graph (

f_{0} =

Threshold frequency)

Question Image

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

The surface of certain metal is first illuminated with light of wavelength

λ_{1} = 350 n m

and then, by a light of wavelength

λ_{2} = 540 n m .

It is found that the maximum speed of the photoelectrons in the two cases differ by a factor of

2

. The work function of the metal (in

e V

) is close to
(Energy of photon

= \frac{1240}{λ (i n n m)} e V

)

HARD

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

In a photoelectric experiment, a parallel beam of monochromatic light with the power of

200 W

is incident on a perfectly absorbing cathode of work function

6.25 eV

. The frequency of light is just above the threshold frequency so that the photoelectrons are emitted with negligible kinetic energy. Assume that the photoelectron emission efficiency is 100%. A potential difference of

500 V

is applied between the cathode and the anode. All the emitted electrons are incident normally on the anode and are absorbed. The anode experiences a force

F = n \times 10^{- 4} N

due to the impact of the electrons. The value of

n

is __________. Mass of the electron

m_{e} = 9 \times 10^{- 31} kg a n d 1.0 eV = 1.6 \times 10^{- 19} J

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

In a photoelectric effect measurement, the stopping potential for a given metal is found to be

V_{0}

volt

when radiation of wavelength

λ_{0}

is used. If radiation of wavelength

{2 λ}_{0}

is used with the same metal then the stopping potential (in

volt

) will be

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

Light of wavelength

500 nm

is incident on a metal with work function

2.28 eV

. The de Broglie wavelength of the emitted electron is:

HARD

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

Explain the working of photo emissive cell. Write any two applications of photoelectric cells.

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

The anode voltage of a photocell is kept fixed. The wavelength

λ

of the light falling on the cathode is gradually changed. The plate current

I

of the photocell varies as follows :

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

Photons with energy of

5 eV

are incident on a cathode,

C

in a photoelectric cell. The maximum energy of emitted photoelectrons is

2 eV.

When photons of energy

6 eV

are incident on

C

, no photoelectrons will reach the anode,

A

, if, the stopping potential of

A

relative to

C

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

When a certain metallic surface is illuminated with monochromatic light of wavelength

λ,

the stopping potential for photoelectric current is

3 V_{0}

and when the same surface is illuminated with light of wavelength

2 λ,

the stopping potential is

V_{0} .

The threshold wavelength of this surface for photoelectric effect is

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

When a metallic surface is illuminated with radiation of wavelength

λ

, the stopping potential is

V

. If the same surface is illuminated with radiation of wavelength

2 λ

, the stopping potential is

\frac{V}{4}

. The threshold wavelength for the metallic surface is:

EASY

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

Which of the following does not support the wave nature of light?

MEDIUM

Physics>Modern Physics>Dual Nature of Radiation and Atomic Physics>Photo Cells and their Applications

When the light of frequency

2 ν_{0}

(where

ν_{0}

is threshold frequency), is incident on a metal plate, the maximum velocity of electrons emitted is

v_{1}

. When the frequency of the incident radiation is increased to

5 ν_{0},

the maximum velocity of electrons emitted from the same plate is

v_{2} .

The ratio of

v_{1} t o v_{2}

List the applications of photoelectric effect.

Important Questions on Dual Nature of Radiation and Atomic Physics

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